When refiling a reference electrode with an internal solution, an error occurs in the output value of a measuring instrument. The reason for this is as follows.
A silver/silver chloride electrode used as the reference electrode is one in which a silver chloride layer is formed by such as electrodeposition around a rod-shaped or plate-shaped core material made of silver.
The reference potential of the silver/silver chloride electrode is known to depend on the concentration of chloride ions in the internal solution. However, when silver ions are eluted through cracks and/or the like present in the silver chloride layer, the surrounding silver chloride is reduced to release chloride ions into the internal solution, and therefore the chloride ion concentration in the internal solution is slightly changed to change the reference potential of the silver/silver chloride electrode.
The change in the reference potential is stabilized when the silver ions are saturated in the internal solution. However, when refilling a new internal solution, the elution of silver ions again occurs from an internal electrode to change the reference potential, and as a result, every time the internal solution is refilled, an error occurs in the measured value of the measuring instrument.
In the past, when measuring a sample that is stored in a container and has a constant characteristic value, an internal solution has been refilled before the measurement, and the sample has been measured after the output value of a measuring instrument was stabilized.
However, when refilling an internal solution during sample measurement, in particular, when continuously measuring a sample whose measured value keeps changing or samples supplied one after another, an error in a measured value due to refilling the internal solution becomes a big problem.